The present invention relates to a charged beam applying apparatus utilizing charged particles such as electrons and ions and, in particular, to a charged beam applying apparatus equipped with a cleaning function and adapted to clean off a contamination through the utilization of an oxidation effect.
The photo-lithography technique mainly so far utilized as a fine pattern forming technique has been indicated, in recent years, as having a limitation on its use in those integrated circuits of a high integration density. In order to overcome such a limitation, an electron beam lithography has been quickly advanced for an electron beam exposure apparatus. In the electronic beam exposure apparatus, an electron beam emitted from an electron gun is deflected/controlled by an electrooptical system column so that a desired pattern is described on a specimen. Here, the expression "deflection" is intended to mean the changing of an electron beam path by an electrostatic field or magnetic field for instance and the expression "control" is intended to mean the focusing or shaping of the beam by an electromagnetic lens, electrostatic lens or a deflection (magnetic field, an electrostatic field) for instance. In this type of electronic beam exposure a deflection means apparatus, a hydrocarbon-based contamination is deposited on the deflection electrode sleeve, aperture, etc., through a reaction of a residual gas in the presence of scattered electrons. When the contamination is electrically charged, there arises a deflection error or aberration so that an image is described with lowered accuracy. This contamination is deposited on the electrode, sleeve, aperture, etc., even if the degree of vacuum is a high vacuum of the order of 10.sup.-9 Torrs.
With the contamination heavily deposited, the deflection error of the beam increased and image description accuracy much lowered, it is necessary to remove such contamination. In order to remove the contamination, the convention method comprises detaching the column, taking out those contaminated component parts or either cleaning them or replacing them with new component parts. This method, however, incurs costs resulting from the detachment, etc., of the column or involves a fall in operation efficiency, thus presenting a problem.
In order to suppress such a problem, the so-called in-situ cleaning technique has been newly developed which involves the detachment of the column. Such a typical in-situ cleaning method comprises utilizing an oxidation process.
Even if, therefore, the contamination is removed, there still arises a minute deflection error. It is expected that such a deflection error, being very small, will provide a possible future bar to the formation of a very fine pattern.
This may be caused by the oxide film produced by the cleaning method utilizing the oxidation process. The oxide film, being electrically charged, produces a deflection error.
Further, a native oxide film normally exists on the surface of a metal and, if being electrically charged, will produce a deflection error.
With respect to these problems it has been experimentally confirmed by the inventors that it is effective to make up component parts in the column with the use of Au or Pt. The reason is that the use of the Au or Pt involves no formation of the native oxide film and that it is simpler to remove the oxide film.
The Au or Pt is very high in cost and low in manufacturing accuracy. It may be considered that, in order to solve these problems, the Au be plated or evaporated on the surface of, for example, Ni. The solution to this problem is complex in process and, in addition, there also arises the problem that, due to the outer surface exposure of the Ni through a diffusion, an oxide film is formed on a surface.
It is, therefore, requested that the component parts of the column be formed with the use of a less charged material except for the Au and Pt. However, the relation of the material and electric charging, as well as that of the electric charging and deflection error, is unclear and there has existed no proper standard on which the material is used.
It has not thus far been possible to select any material for eliminating or reducing a deflection error resulting from the electric charging of the oxide film caused by the cleaning using the oxidation process.
It has been found that the down-flow process by a N.sub.2 gas is effective to remove the oxide film of the Au and Pt. However, no clarification has been given about the conditions under which the down-flow process is effected with the N.sub.2 gas. It has not been possible to remove the oxide film properly.
Further, not only the hydrocarbon-based contamination but also other substances are present in actual practice in the column. This very event goes undetected in the conventional cleaning method.
The same thing is also true of an electron beam exposure apparatus, ion beam exposure apparatus, and not only the exposure apparatus but also various types of charged beam applying apparatuses for scanning a specimen with the charged beam.